1. Field of the Invention
Aspects of the present invention relate to a liquid fuel cartridge, and more particularly, to a liquid fuel cartridge having a bistable structure that allows for the amount of liquid fuel remaining in the cartridge to be determined.
2. Description of the Related Art
A direct liquid feed fuel cell is an apparatus that generates electricity via electrochemical reactions between a liquid organic fuel, such as methanol or ethanol, and an oxidant, i.e., oxygen. The electricity generated by the direct liquid feed fuel cell has high specific energy density and high current density. Also, since a liquid fuel, i.e., methanol, is directly fed to the cell, the direct feed fuel cell does not require a peripheral device such as a fuel reformer, and storing and supplying the liquid fuel are easy.
As depicted in FIG. 1, the direct feed fuel cell has a structure including an anode electrode 2, a cathode electrode 3, and an electrolyte membrane 1 interposed between the two electrodes 2 and 3. The anode electrode 2 includes a diffusion layer 22 for supplying and diffusing a fuel, a catalyst layer 21 at which oxidation and reduction reactions of the fuel occur, and an electrode supporting layer 23. The cathode electrode 3 also includes a diffusion layer 32 for supplying and diffusing the fuel, a catalyst layer 31 on which oxidation and reduction reactions of the fuel occur, and an electrode supporting layer 33. The catalyst for generating the electrode reaction is formed of a precious metal, such as platinum, having a superior catalytic characteristic at low temperature. Alternately, to avoid catalyst poisoning by CO, which is a by-product from the electrode reaction, a transition metal alloy catalyst, comprising ruthenium, rhodium, osmium, or nickel can be used. The electrode supporting layers 23 and 33 can be made of a water-proofed carbon paper or water-proofed carbon fiber for easy supplying of fuel and discharging reaction products. The electrolyte membrane 1 is a hydrogen ion exchange membrane having ion conductivity and containing moisture, and is formed of a polymer membrane having a thickness of 50˜200 μm.
An electrode reaction of a direct methanol fuel cell (DMFC), which is a direct liquid feed fuel cell, includes an anode reaction where fuel is oxidized and a cathode reaction where hydrogen and oxygen are reduced, as described below.CH3OH+H2O→CO2+6H++6e− (Anode reaction)  [Reaction 1]3/2 O2+6H++6e−→3H2O (Cathode reaction)  [Reaction 2]CH3OH+3/2 O2→2H2O+CO2 (Overall reaction)  [Reaction 3]
Carbon dioxide, hydrogen ions, and electrons are produced at the anode electrode 2 where the fuel is oxidized (reaction 1). The produced hydrogen ions migrate to the cathode electrode 3 through a hydrogen ion exchange membrane 1. Water is produced by the reduction reaction between hydrogen ions, electrons transferred from an external circuit, and oxygen at the cathode electrode 3 (reaction 2). Accordingly, water and carbon dioxide are produced as the result of an overall electrochemical reaction (reaction 3) between methanol and oxygen, and two moles of water are produced for each mole of methanol that reacts with oxygen.
Fuels used in a fuel cell may be stored in a separated fuel tank or in a replaceable cartridge. When a conventional cartridge is used, in order to know the amount of fuel remaining in the cartridge, the flowrate of the fuel pump in use and the amount of fuel stored in the cartridge must be known. However, the flowrate of the pump varies according to the pressure change in the cartridge and the amount of fuel remaining in the cartridge. Accordingly, a device that reliably indicates the amount of fuel remaining in a liquid fuel cartridge is needed.